The Aether is out for 1.2.5!

See here
Granted it's still a pre-release but it's out and it's Forge based. Took a while but I got the standard mod set I run working without problems. Note Aether doesn't appear to obey it's configs so I had to restart (no biggie here for me.. was basically done with the other world) as I was getting serious Block ID conflicts.
Also had to abuse the hell out of the integrated 4096 fix where I didn't before. Used most of the 400-480 range. (400-~1200 is free)